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+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE.   *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE Theora SOURCE CODE IS COPYRIGHT (C) 2002-2009                *
+ * by the Xiph.Org Foundation http://www.xiph.org/                  *
+ *                                                                  *
+ ********************************************************************
+
+  function:
+  last mod: $Id: theora.h,v 1.8 2004/03/15 22:17:32 derf Exp $
+
+ ********************************************************************/
+
+/**\mainpage
+ * 
+ * \section intro Introduction
+ *
+ * This is the documentation for <tt>libtheora</tt> C API.
+ * The current reference
+ * implementation for <a href="http://www.theora.org/">Theora</a>, a free,
+ * patent-unencumbered video codec.
+ * Theora is derived from On2's VP3 codec with additional features and
+ *  integration with Ogg multimedia formats by
+ *  <a href="http://www.xiph.org/">the Xiph.Org Foundation</a>.
+ * Complete documentation of the format itself is available in
+ * <a href="http://www.theora.org/doc/Theora.pdf">the Theora
+ *  specification</a>.
+ *
+ * \subsection Organization
+ *
+ * The functions documented here are actually subdivided into three 
+ * separate libraries:
+ * - <tt>libtheoraenc</tt> contains the encoder interface,
+ *   described in \ref encfuncs.
+ * - <tt>libtheoradec</tt> contains the decoder interface and
+ *   routines shared with the encoder.
+ *   You must also link to this if you link to <tt>libtheoraenc</tt>.
+ *   The routines in this library are described in \ref decfuncs and 
+ *   \ref basefuncs.
+ * - <tt>libtheora</tt> contains the \ref oldfuncs.
+ *
+ * New code should link to <tt>libtheoradec</tt> and, if using encoder
+ * features, <tt>libtheoraenc</tt>. Together these two export both
+ * the standard and the legacy API, so this is all that is needed by
+ * any code. The older <tt>libtheora</tt> library is provided just for
+ * compatibility with older build configurations.
+ *
+ * In general the recommended 1.x API symbols can be distinguished
+ * by their <tt>th_</tt> or <tt>TH_</tt> namespace prefix.
+ * The older, legacy API uses <tt>theora_</tt> or <tt>OC_</tt>
+ * prefixes instead.
+ */
+
+/**\file
+ * The shared <tt>libtheoradec</tt> and <tt>libtheoraenc</tt> C API.
+ * You don't need to include this directly.*/
+
+#if !defined(_O_THEORA_CODEC_H_)
+# define _O_THEORA_CODEC_H_ (1)
+# include <ogg/ogg.h>
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+
+
+/**\name Return codes*/
+/*@{*/
+/**An invalid pointer was provided.*/
+#define TH_EFAULT     (-1)
+/**An invalid argument was provided.*/
+#define TH_EINVAL     (-10)
+/**The contents of the header were incomplete, invalid, or unexpected.*/
+#define TH_EBADHEADER (-20)
+/**The header does not belong to a Theora stream.*/
+#define TH_ENOTFORMAT (-21)
+/**The bitstream version is too high.*/
+#define TH_EVERSION   (-22)
+/**The specified function is not implemented.*/
+#define TH_EIMPL      (-23)
+/**There were errors in the video data packet.*/
+#define TH_EBADPACKET (-24)
+/**The decoded packet represented a dropped frame.
+   The player can continue to display the current frame, as the contents of the
+    decoded frame buffer have not changed.*/
+#define TH_DUPFRAME   (1)
+/*@}*/
+
+/**The currently defined color space tags.
+ * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
+ *  specification</a>, Chapter 4, for exact details on the meaning
+ *  of each of these color spaces.*/
+typedef enum{
+  /**The color space was not specified at the encoder.
+      It may be conveyed by an external means.*/
+  TH_CS_UNSPECIFIED,
+  /**A color space designed for NTSC content.*/
+  TH_CS_ITU_REC_470M,
+  /**A color space designed for PAL/SECAM content.*/
+  TH_CS_ITU_REC_470BG,
+  /**The total number of currently defined color spaces.*/
+  TH_CS_NSPACES
+}th_colorspace;
+
+/**The currently defined pixel format tags.
+ * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
+ *  specification</a>, Section 4.4, for details on the precise sample
+ *  locations.*/
+typedef enum{
+  /**Chroma decimation by 2 in both the X and Y directions (4:2:0).
+     The Cb and Cr chroma planes are half the width and half the
+      height of the luma plane.*/
+  TH_PF_420,
+  /**Currently reserved.*/
+  TH_PF_RSVD,
+  /**Chroma decimation by 2 in the X direction (4:2:2).
+     The Cb and Cr chroma planes are half the width of the luma plane, but full
+      height.*/
+  TH_PF_422,
+  /**No chroma decimation (4:4:4).
+     The Cb and Cr chroma planes are full width and full height.*/
+  TH_PF_444,
+  /**The total number of currently defined pixel formats.*/
+  TH_PF_NFORMATS
+}th_pixel_fmt;
+
+
+
+/**A buffer for a single color plane in an uncompressed image.
+ * This contains the image data in a left-to-right, top-down format.
+ * Each row of pixels is stored contiguously in memory, but successive
+ *  rows need not be.
+ * Use \a stride to compute the offset of the next row.
+ * The encoder accepts both positive \a stride values (top-down in memory)
+ *  and negative (bottom-up in memory).
+ * The decoder currently always generates images with positive strides.*/
+typedef struct{
+  /**The width of this plane.*/
+  int            width;
+  /**The height of this plane.*/
+  int            height;
+  /**The offset in bytes between successive rows.*/
+  int            stride;
+  /**A pointer to the beginning of the first row.*/
+  unsigned char *data;
+}th_img_plane;
+
+/**A complete image buffer for an uncompressed frame.
+ * The chroma planes may be decimated by a factor of two in either
+ *  direction, as indicated by th_info#pixel_fmt.
+ * The width and height of the Y' plane must be multiples of 16.
+ * They may need to be cropped for display, using the rectangle
+ *  specified by th_info#pic_x, th_info#pic_y, th_info#pic_width,
+ *  and th_info#pic_height.
+ * All samples are 8 bits.
+ * \note The term YUV often used to describe a colorspace is ambiguous.
+ * The exact parameters of the RGB to YUV conversion process aside, in
+ *  many contexts the U and V channels actually have opposite meanings.
+ * To avoid this confusion, we are explicit: the name of the color
+ *  channels are Y'CbCr, and they appear in that order, always.
+ * The prime symbol denotes that the Y channel is non-linear.
+ * Cb and Cr stand for "Chroma blue" and "Chroma red", respectively.*/
+typedef th_img_plane th_ycbcr_buffer[3];
+
+/**Theora bitstream information.
+ * This contains the basic playback parameters for a stream, and corresponds to 
+ *  the initial 'info' header packet.
+ * To initialize an encoder, the application fills in this structure and
+ *  passes it to th_encode_alloc().
+ * A default encoding mode is chosen based on the values of the #quality and
+ *  #target_bitrate fields.
+ * On decode, it is filled in by th_decode_headerin(), and then passed to
+ *  th_decode_alloc().
+ *
+ * Encoded Theora frames must be a multiple of 16 in size;
+ *  this is what the #frame_width and #frame_height members represent.
+ * To handle arbitrary picture sizes, a crop rectangle is specified in the
+ *  #pic_x, #pic_y, #pic_width and #pic_height members.
+ *
+ * All frame buffers contain pointers to the full, padded frame.
+ * However, the current encoder <em>will not</em> reference pixels outside of
+ *  the cropped picture region, and the application does not need to fill them
+ *  in.
+ * The decoder <em>will</em> allocate storage for a full frame, but the
+ *  application <em>should not</em> rely on the padding containing sensible
+ *  data.
+ *
+ * It is also generally recommended that the offsets and sizes should still be
+ *  multiples of 2 to avoid chroma sampling shifts when chroma is sub-sampled.
+ * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
+ *  specification</a>, Section 4.4, for more details.
+ *
+ * Frame rate, in frames per second, is stored as a rational fraction, as is
+ *  the pixel aspect ratio.
+ * Note that this refers to the aspect ratio of the individual pixels, not of
+ *  the overall frame itself.
+ * The frame aspect ratio can be computed from pixel aspect ratio using the
+ *  image dimensions.*/
+typedef struct{
+  /**\name Theora version
+   * Bitstream version information.*/
+  /*@{*/
+  unsigned char version_major;
+  unsigned char version_minor;
+  unsigned char version_subminor;
+  /*@}*/
+  /**The encoded frame width.
+   * This must be a multiple of 16, and less than 1048576.*/
+  ogg_uint32_t  frame_width;
+  /**The encoded frame height.
+   * This must be a multiple of 16, and less than 1048576.*/
+  ogg_uint32_t  frame_height;
+  /**The displayed picture width.
+   * This must be no larger than width.*/
+  ogg_uint32_t  pic_width;
+  /**The displayed picture height.
+   * This must be no larger than height.*/
+  ogg_uint32_t  pic_height;
+  /**The X offset of the displayed picture.
+   * This must be no larger than #frame_width-#pic_width or 255, whichever is
+   *  smaller.*/
+  ogg_uint32_t  pic_x;
+  /**The Y offset of the displayed picture.
+   * This must be no larger than #frame_height-#pic_height, and
+   *  #frame_height-#pic_height-#pic_y must be no larger than 255.
+   * This slightly funny restriction is due to the fact that the offset is
+   *  specified from the top of the image for consistency with the standard
+   *  graphics left-handed coordinate system used throughout this API, while
+   *  it is stored in the encoded stream as an offset from the bottom.*/
+  ogg_uint32_t  pic_y;
+  /**\name Frame rate
+   * The frame rate, as a fraction.
+   * If either is 0, the frame rate is undefined.*/
+  /*@{*/
+  ogg_uint32_t  fps_numerator;
+  ogg_uint32_t  fps_denominator;
+  /*@}*/
+  /**\name Aspect ratio
+   * The aspect ratio of the pixels.
+   * If either value is zero, the aspect ratio is undefined.
+   * If not specified by any external means, 1:1 should be assumed.
+   * The aspect ratio of the full picture can be computed as
+   * \code
+   *  aspect_numerator*pic_width/(aspect_denominator*pic_height).
+   * \endcode */
+  /*@{*/
+  ogg_uint32_t  aspect_numerator;
+  ogg_uint32_t  aspect_denominator;
+  /*@}*/
+  /**The color space.*/
+  th_colorspace colorspace;
+  /**The pixel format.*/
+  th_pixel_fmt  pixel_fmt;
+  /**The target bit-rate in bits per second.
+     If initializing an encoder with this struct, set this field to a non-zero
+      value to activate CBR encoding by default.*/
+  int           target_bitrate;
+  /**The target quality level.
+     Valid values range from 0 to 63, inclusive, with higher values giving
+      higher quality.
+     If initializing an encoder with this struct, and #target_bitrate is set
+      to zero, VBR encoding at this quality will be activated by default.*/
+  /*Currently this is set so that a qi of 0 corresponds to distortions of 24
+     times the JND, and each increase by 16 halves that value.
+    This gives us fine discrimination at low qualities, yet effective rate
+     control at high qualities.
+    The qi value 63 is special, however.
+    For this, the highest quality, we use one half of a JND for our threshold.
+    Due to the lower bounds placed on allowable quantizers in Theora, we will
+     not actually be able to achieve quality this good, but this should
+     provide as close to visually lossless quality as Theora is capable of.
+    We could lift the quantizer restrictions without breaking VP3.1
+     compatibility, but this would result in quantized coefficients that are
+     too large for the current bitstream to be able to store.
+    We'd have to redesign the token syntax to store these large coefficients,
+     which would make transcoding complex.*/
+  int           quality;
+  /**The amount to shift to extract the last keyframe number from the granule
+   *  position.
+   * This can be at most 31.
+   * th_info_init() will set this to a default value (currently <tt>6</tt>,
+   *  which is good for streaming applications), but you can set it to 0 to
+   *  make every frame a keyframe.
+   * The maximum distance between key frames is
+   *  <tt>1<<#keyframe_granule_shift</tt>.
+   * The keyframe frequency can be more finely controlled with
+   *  #TH_ENCCTL_SET_KEYFRAME_FREQUENCY_FORCE, which can also be adjusted
+   *  during encoding (for example, to force the next frame to be a keyframe),
+   *  but it cannot be set larger than the amount permitted by this field after
+   *  the headers have been output.*/
+  int           keyframe_granule_shift;
+}th_info;
+
+/**The comment information.
+ *
+ * This structure holds the in-stream metadata corresponding to
+ *  the 'comment' header packet.
+ * The comment header is meant to be used much like someone jotting a quick
+ *  note on the label of a video.
+ * It should be a short, to the point text note that can be more than a couple
+ *  words, but not more than a short paragraph.
+ *
+ * The metadata is stored as a series of (tag, value) pairs, in
+ *  length-encoded string vectors.
+ * The first occurrence of the '=' character delimits the tag and value.
+ * A particular tag may occur more than once, and order is significant.
+ * The character set encoding for the strings is always UTF-8, but the tag
+ *  names are limited to ASCII, and treated as case-insensitive.
+ * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
+ *  specification</a>, Section 6.3.3 for details.
+ *
+ * In filling in this structure, th_decode_headerin() will null-terminate
+ *  the user_comment strings for safety.
+ * However, the bitstream format itself treats them as 8-bit clean vectors,
+ *  possibly containing null characters, and so the length array should be
+ *  treated as their authoritative length.
+ */
+typedef struct th_comment{
+  /**The array of comment string vectors.*/
+  char **user_comments;
+  /**An array of the corresponding length of each vector, in bytes.*/
+  int   *comment_lengths;
+  /**The total number of comment strings.*/
+  int    comments;
+  /**The null-terminated vendor string.
+     This identifies the software used to encode the stream.*/
+  char  *vendor;
+}th_comment;
+
+
+
+/**A single base matrix.*/
+typedef unsigned char th_quant_base[64];
+
+/**A set of \a qi ranges.*/
+typedef struct{
+  /**The number of ranges in the set.*/
+  int                  nranges;
+  /**The size of each of the #nranges ranges.
+     These must sum to 63.*/
+  const int           *sizes;
+  /**#nranges <tt>+1</tt> base matrices.
+     Matrices \a i and <tt>i+1</tt> form the endpoints of range \a i.*/
+  const th_quant_base *base_matrices;
+}th_quant_ranges;
+
+/**A complete set of quantization parameters.
+   The quantizer for each coefficient is calculated as:
+   \code
+    Q=MAX(MIN(qmin[qti][ci!=0],scale[ci!=0][qi]*base[qti][pli][qi][ci]/100),
+     1024).
+   \endcode
+
+   \a qti is the quantization type index: 0 for intra, 1 for inter.
+   <tt>ci!=0</tt> is 0 for the DC coefficient and 1 for AC coefficients.
+   \a qi is the quality index, ranging between 0 (low quality) and 63 (high
+    quality).
+   \a pli is the color plane index: 0 for Y', 1 for Cb, 2 for Cr.
+   \a ci is the DCT coefficient index.
+   Coefficient indices correspond to the normal 2D DCT block
+    ordering--row-major with low frequencies first--\em not zig-zag order.
+
+   Minimum quantizers are constant, and are given by:
+   \code
+   qmin[2][2]={{4,2},{8,4}}.
+   \endcode
+
+   Parameters that can be stored in the bitstream are as follows:
+    - The two scale matrices ac_scale and dc_scale.
+      \code
+      scale[2][64]={dc_scale,ac_scale}.
+      \endcode
+    - The base matrices for each \a qi, \a qti and \a pli (up to 384 in all).
+      In order to avoid storing a full 384 base matrices, only a sparse set of
+       matrices are stored, and the rest are linearly interpolated.
+      This is done as follows.
+      For each \a qti and \a pli, a series of \a n \a qi ranges is defined.
+      The size of each \a qi range can vary arbitrarily, but they must sum to
+       63.
+      Then, <tt>n+1</tt> matrices are specified, one for each endpoint of the
+       ranges.
+      For interpolation purposes, each range's endpoints are the first \a qi
+       value it contains and one past the last \a qi value it contains.
+      Fractional values are rounded to the nearest integer, with ties rounded
+       away from zero.
+
+      Base matrices are stored by reference, so if the same matrices are used
+       multiple times, they will only appear once in the bitstream.
+      The bitstream is also capable of omitting an entire set of ranges and
+       its associated matrices if they are the same as either the previous
+       set (indexed in row-major order) or if the inter set is the same as the
+       intra set.
+
+    - Loop filter limit values.
+      The same limits are used for the loop filter in all color planes, despite
+       potentially differing levels of quantization in each.
+
+   For the current encoder, <tt>scale[ci!=0][qi]</tt> must be no greater
+    than <tt>scale[ci!=0][qi-1]</tt> and <tt>base[qti][pli][qi][ci]</tt> must
+    be no greater than <tt>base[qti][pli][qi-1][ci]</tt>.
+   These two conditions ensure that the actual quantizer for a given \a qti,
+    \a pli, and \a ci does not increase as \a qi increases.
+   This is not required by the decoder.*/
+typedef struct{
+  /**The DC scaling factors.*/
+  ogg_uint16_t    dc_scale[64];
+  /**The AC scaling factors.*/
+  ogg_uint16_t    ac_scale[64];
+  /**The loop filter limit values.*/
+  unsigned char   loop_filter_limits[64];
+  /**The \a qi ranges for each \a ci and \a pli.*/
+  th_quant_ranges qi_ranges[2][3];
+}th_quant_info;
+
+
+
+/**The number of Huffman tables used by Theora.*/
+#define TH_NHUFFMAN_TABLES (80)
+/**The number of DCT token values in each table.*/
+#define TH_NDCT_TOKENS     (32)
+
+/**A Huffman code for a Theora DCT token.
+ * Each set of Huffman codes in a given table must form a complete, prefix-free
+ *  code.
+ * There is no requirement that all the tokens in a table have a valid code,
+ *  but the current encoder is not optimized to take advantage of this.
+ * If each of the five grouops of 16 tables does not contain at least one table
+ *  with a code for every token, then the encoder may fail to encode certain
+ *  frames.
+ * The complete table in the first group of 16 does not have to be in the same
+ *  place as the complete table in the other groups, but the complete tables in
+ *  the remaining four groups must all be in the same place.*/
+typedef struct{
+  /**The bit pattern for the code, with the LSbit of the pattern aligned in
+   *   the LSbit of the word.*/
+  ogg_uint32_t pattern;
+  /**The number of bits in the code.
+   * This must be between 0 and 32, inclusive.*/
+  int          nbits;
+}th_huff_code;
+
+
+
+/**\defgroup basefuncs Functions Shared by Encode and Decode*/
+/*@{*/
+/**\name Basic shared functions*/
+/*@{*/
+/**Retrieves a human-readable string to identify the library vendor and
+ *  version.
+ * \return the version string.*/
+extern const char *th_version_string(void);
+/**Retrieves the library version number.
+ * This is the highest bitstream version that the encoder library will produce,
+ *  or that the decoder library can decode.
+ * This number is composed of a 16-bit major version, 8-bit minor version
+ * and 8 bit sub-version, composed as follows:
+ * \code
+ * (VERSION_MAJOR<<16)+(VERSION_MINOR<<8)+(VERSION_SUBMINOR)
+ * \endcode
+ * \return the version number.*/
+extern ogg_uint32_t th_version_number(void);
+/**Converts a granule position to an absolute frame index, starting at
+ *  <tt>0</tt>.
+ * The granule position is interpreted in the context of a given
+ *  #th_enc_ctx or #th_dec_ctx handle (either will suffice).
+ * \param _encdec  A previously allocated #th_enc_ctx or #th_dec_ctx
+ *                  handle.
+ * \param _granpos The granule position to convert.
+ * \returns The absolute frame index corresponding to \a _granpos.
+ * \retval -1 The given granule position was invalid (i.e. negative).*/
+extern ogg_int64_t th_granule_frame(void *_encdec,ogg_int64_t _granpos);
+/**Converts a granule position to an absolute time in seconds.
+ * The granule position is interpreted in the context of a given
+ *  #th_enc_ctx or #th_dec_ctx handle (either will suffice).
+ * \param _encdec  A previously allocated #th_enc_ctx or #th_dec_ctx
+ *                  handle.
+ * \param _granpos The granule position to convert.
+ * \return The absolute time in seconds corresponding to \a _granpos.
+ *         This is the "end time" for the frame, or the latest time it should
+ *          be displayed.
+ *         It is not the presentation time.
+ * \retval -1 The given granule position was invalid (i.e. negative).*/
+extern double th_granule_time(void *_encdec,ogg_int64_t _granpos);
+/**Determines whether a Theora packet is a header or not.
+ * This function does no verification beyond checking the packet type bit, so
+ *  it should not be used for bitstream identification; use
+ *  th_decode_headerin() for that.
+ * As per the Theora specification, an empty (0-byte) packet is treated as a
+ *  data packet (a delta frame with no coded blocks).
+ * \param _op An <tt>ogg_packet</tt> containing encoded Theora data.
+ * \retval 1 The packet is a header packet
+ * \retval 0 The packet is a video data packet.*/
+extern int th_packet_isheader(ogg_packet *_op);
+/**Determines whether a theora packet is a key frame or not.
+ * This function does no verification beyond checking the packet type and
+ *  key frame bits, so it should not be used for bitstream identification; use
+ *  th_decode_headerin() for that.
+ * As per the Theora specification, an empty (0-byte) packet is treated as a
+ *  delta frame (with no coded blocks).
+ * \param _op An <tt>ogg_packet</tt> containing encoded Theora data.
+ * \retval 1  The packet contains a key frame.
+ * \retval 0  The packet contains a delta frame.
+ * \retval -1 The packet is not a video data packet.*/
+extern int th_packet_iskeyframe(ogg_packet *_op);
+/*@}*/
+
+
+/**\name Functions for manipulating header data*/
+/*@{*/
+/**Initializes a th_info structure.
+ * This should be called on a freshly allocated #th_info structure before
+ *  attempting to use it.
+ * \param _info The #th_info struct to initialize.*/
+extern void th_info_init(th_info *_info);
+/**Clears a #th_info structure.
+ * This should be called on a #th_info structure after it is no longer
+ *  needed.
+ * \param _info The #th_info struct to clear.*/
+extern void th_info_clear(th_info *_info);
+
+/**Initialize a #th_comment structure.
+ * This should be called on a freshly allocated #th_comment structure
+ *  before attempting to use it.
+ * \param _tc The #th_comment struct to initialize.*/
+extern void th_comment_init(th_comment *_tc);
+/**Add a comment to an initialized #th_comment structure.
+ * \note Neither th_comment_add() nor th_comment_add_tag() support
+ *  comments containing null values, although the bitstream format does
+ *  support them.
+ * To add such comments you will need to manipulate the #th_comment
+ *  structure directly.
+ * \param _tc      The #th_comment struct to add the comment to.
+ * \param _comment Must be a null-terminated UTF-8 string containing the
+ *                  comment in "TAG=the value" form.*/
+extern void th_comment_add(th_comment *_tc, char *_comment);
+/**Add a comment to an initialized #th_comment structure.
+ * \note Neither th_comment_add() nor th_comment_add_tag() support
+ *  comments containing null values, although the bitstream format does
+ *  support them.
+ * To add such comments you will need to manipulate the #th_comment
+ *  structure directly.
+ * \param _tc  The #th_comment struct to add the comment to.
+ * \param _tag A null-terminated string containing the tag  associated with
+ *              the comment.
+ * \param _val The corresponding value as a null-terminated string.*/
+extern void th_comment_add_tag(th_comment *_tc,char *_tag,char *_val);
+/**Look up a comment value by its tag.
+ * \param _tc    An initialized #th_comment structure.
+ * \param _tag   The tag to look up.
+ * \param _count The instance of the tag.
+ *               The same tag can appear multiple times, each with a distinct
+ *                value, so an index is required to retrieve them all.
+ *               The order in which these values appear is significant and
+ *                should be preserved.
+ *               Use th_comment_query_count() to get the legal range for
+ *                the \a _count parameter.
+ * \return A pointer to the queried tag's value.
+ *         This points directly to data in the #th_comment structure.
+ *         It should not be modified or freed by the application, and
+ *          modifications to the structure may invalidate the pointer.
+ * \retval NULL If no matching tag is found.*/
+extern char *th_comment_query(th_comment *_tc,char *_tag,int _count);
+/**Look up the number of instances of a tag.
+ * Call this first when querying for a specific tag and then iterate over the
+ *  number of instances with separate calls to th_comment_query() to
+ *  retrieve all the values for that tag in order.
+ * \param _tc    An initialized #th_comment structure.
+ * \param _tag   The tag to look up.
+ * \return The number on instances of this particular tag.*/
+extern int th_comment_query_count(th_comment *_tc,char *_tag);
+/**Clears a #th_comment structure.
+ * This should be called on a #th_comment structure after it is no longer
+ *  needed.
+ * It will free all memory used by the structure members.
+ * \param _tc The #th_comment struct to clear.*/
+extern void th_comment_clear(th_comment *_tc);
+/*@}*/
+/*@}*/
+
+
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif